How To Dissect Into A 340 Engine - Engine Autopsy

1/25An ugly greasy mess to the uninitiated, but sheer beauty to Mopar fans, a completely stock '70 340. As rare as they are powerful, the 340's performance has become legendary. What did they put out? We'll find out.

Any rebuild starts with tearing down the original engine. Maybe it's the 440 from your GTX; the one that hasn't been run in years and smoked like a hippie at a Dead concert when it did. It could be just a core picked up at the local junkyard that turned over with a breaker bar on the crank. But what's inside? Who knows? In this case, it's the 340 that came in the trunk of a '70 Dart, an original Swinger 340 four-speed. What was the history of this particular smallblock? Its secrets were lost as the car passed, unregistered, from owner to owner over the last ten years, until $750 landed it in our shed. Out of the trunk and on the stand, a careful postmortem of the engine will at least provide some clues on how it died and what it will take to bring it back to life.

While it's tempting to go in and re-engineer one of Chrysler's finest engines for even more power, because of the rarity and historical value of the factory 340 muscle cars, this one will be built as close to dead-nuts stock specs as possible. Resto can be righteous, and that can be reason enough to go stock. With the wide range of speculation, rumors, myths, and even lies that surround stock musclecar engines-especially the 340-we've always wanted to build one stock and put it to the dyno. The factory rated it at 275hp, the automotive press of 30 years ago stated that it felt more like 320, while the NHRA decreed 300 for the '70 340 in Stock Eliminator. Once we settle that debate, we'll dress it out with an aftermarket induction, a modern cam profile no lumpier than the stocker, and headers, just to see what it does.

We'll take a budget approach to the rebuild, cutting costs wherever possible by making use of serviceable parts and keeping the machining operations down to the necessary items. What we won't do is compromise on the items that relate to power production and reliability at high rpm. So the inspection becomes even more important, raising questions that have to be answered before going any further. Are those decks flat enough to hold the head gaskets? Do we install new valve guides? Does the crank get ground? Right now, we'll get inside for a look at what we've got and then decide.